1. Field of the Invention
The present invention relates to a cooling fan controller which cools the interior of a machine such as a computer by forced circulation of air through control of the rotation speed of a cooling fan. More particularly, the invention relates to a cooling fan controller which controls the rotation speed of fan on the basis of an environmental temperature and an output power capacity to a load.
2. Description of the Related Art
In a cooling fan controller cooling the interior of a machine such as a personal computer by forced circulation of air through rotation of a cooling fan, it is the conventional practice to control the rotation speed of the cooling fan through detection of only the environmental temperature in the machine interior by using a temperature detecting element such as thermistor. More specifically, since resistance value of thermistor varies substantially in inverse proportion to a change in the environmental temperature, when the environmental temperature becomes higher and the resistance value of thermistor is reduced, the rotation speed of the fan is increased by increasing driving current fed to a fan motor. When an increase in the resistance value of the thermistor is caused by a decrease in the environmental temperature, the rotation speed of the fan is reduced by reducing the driving current fed to the fan motor.
The environmental temperature in a machine is caused by heat production resulting from power loss occurring upon operation of circuit units or devices fed with power. There is therefore a time lag to some extent before a change in the environmental temperature. In the conventional temperature. In the conventional cooling fan controller controlling the rotation speed of the cooling fan by detection of the environmental temperature alone by means of thermistor, therefore, a considerable heat generation of the load may lead to a large increase in temperature in the machine as a result of a delay in control of the rotation speed of the fan by acting on the environmental temperature, and this may take much time. It is therefore necessary to adopt a rotation heat sink larger in size used in the circuit or the machine and to use parts of a higher rating in terms of standard value relative to the environmental temperature for the parts, taking account of the temperature increase caused by a delay in cooling, thus forming a cause of a higher cost.
According to the present invention, there is provided a cooling fan controller permitting effective cooling without causing a delay in time by accurately detecting factors of a sudden heat generation.
The invention relates to a cooling fan controller which cools the interior of a machine by forced circulation of air under control of the rotation speed (revolutions) of a cooling fan, comprising a first fan control circuit which controls the rotation speed of the cooling fan in response to the environmental temperature; and a second fan control circuit which detects the output power capacity of a power supplying section supplying power to a load, and which, when the output power capacity is under a prescribed threshold value, allows control of the cooling fan in response to the environmental temperature by the fist fan control circuit, and when the output power capacity is at least the prescribed threshold value, disables cooling fan control in response to the environmental temperature by the fan control circuit to control the same at a prescribed maximum rotation speed. As a result, in the cooling fan controller of the invention, when there is an increase in the output power capacity from the power supply circuit to a load at a low environmental temperature in a machine, cooling based on a sufficient forced circulation of air is started before an increase in the environmental temperature resulting from heat generation of the load, and it is possible to ensure prevention of a large increase in environmental temperature caused by a delay in cooling. It is therefore possible to inhibit increase in temperature of a machine or parts used in a machine, reduce the rating of the parts employed, reduce the size of a radiation heat sink, and thus reduce the cost of the machine. The first fan control circuit is a circuit which supplies a driving current substantially proportional to the environmental temperature detected with a temperature detecting element such as thermistor to a fan motor. The second fan control circuit has a comparing circuit which causes supply of a current to the fan motor in response to the environmental temperature based on the first fan control circuit with an L-level output when the detected value of the output current capacity of the power supply circuit is under a prescribed threshold value, and disables control of the cooling fan in response to the environmental temperature of the first fan control circuit with an H-level output when the detected value is at least the prescribed threshold value, to cause supply of a prescribed maximum driving current to the fan motor. The second fan control circuit has a differential amplifying circuit which amplifies a detection signal of the output current capacity of the power supply circuit in the first half stage of the comparing circuit. The first fan control circuit comprises a first transistor which feeds collector current substantially proportional to a change in the resistance value of thermistor inversely proportional to temperature, and a second transistor which receives supply of base current obtained by subtracting the collector current of the first transistor from the prescribed bias current and supplies collector current to the fan motor; causes a change in collector current in response to the resistance value of the thermistor by biassing the base of the first transistor in the forward direction with an H-level output of the second fan control circuit; brings the collector current to zero by cutting off the base of the first transistor by reverse direction bias with an L-level output of the second fan control circuit; and fixes the collector current of the second transistor at a prescribed maximum current. Any of the following embodiments is applicable for detecting the output power capacity fed from the power supply circuit to the load. The second control circuit detects current supplied from the power supply circuit to the load and compares the detected current with a prescribed threshold value. When the power supply circuit is a switching regulator, the second fan control circuit detects voltage of a secondary-side winding of a transformer provided in the switching regulator and compares the detected voltage with a prescribed threshold value. Furthermore, when the power supply circuit is a switching regulator, the second fan control circuit detects current fed by a switching element such as an EFT provided in the switching regulator to a primary-side winding of a transformer and compares the detected current with a prescribed threshold value. When the power supply circuit is a switching regulator, furthermore, the second fan control circuit detects input voltage to a primary-side winding of a transformer provided in the switching regulator.
In other words, the cooling fan controller of the invention comprises an output detecting unit detecting the output capacity to a load; a temperature detecting unit detecting environmental temperature; and a control unit which controls the rotation speed of a cooling fan on the basis of the output capacity and the environmental temperature, and when the output capacity is under a prescribed value, invalidates the control based on the environmental temperature. In this case, when the output capacity is at least a prescribed value, the control unit invalidates the control based on the environmental temperature, and controls the cooling fan at a prescribed maximum rotation speed.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description with reference to the drawings.